<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">
        <div id="one">hello world</div>
    </div>
    <script>
        var app = document.getElementById("app")
        var one = document.getElementById("one")
        var test = one.cloneNode(true)
        console.log(test);
        app.appendChild(test)
        console.log(app);
    </script>
</body>
</html>